The present invention relates generally to equipment used in oilfield and, more particularly, to a hydraulic actuator for a valve.
Hydraulic actuators are used in the petroleum industry to open and close valves. Subsea actuators are used to operate valves for pipelines and drilling operations under water. A prior art actuator 2 is shown in schematic form in FIG. 1A. The actuator 2 is coupled to and adapted to control a valve 8 for a pipeline 9. The actuator 2 is coupled to a control system 6 which may comprise a hydraulic three-way valve, for example. The actuator 2, control system 6 and hydraulic lines coupled therebetween are submerged in seawater. A hydrostatic head 7 comprises pressure generated due to the height of the fluid column at a given depth under the water surface 5. For example, the hydrostatic head 7 generated by seawater at 10,000 feet depth is 0.433 p.s.i./footxc3x9710,000 feet=4,333 p.s.i. The amount of pressure generated is dependent on the type of fluid in the column. For example, hydraulic fluid generates less pressure than seawater. Hydraulic fluid may be pumped into the control system 6 through a hydraulic control line coupled from the water surface 5 to the control system 6 at an input port I.
The actuator 2 includes a spring 4 adapted to exert pressure on a piston 3. The piston 3 may be sealed with o-rings inside the actuator housing. The control system 6 is coupled to the actuator 2 at port P1 in a region above the piston 3, and also is coupled to the actuator 2 at port P2 in a region below the piston 3, for example, with hydraulic lines. Hydraulic fluid may be sent from the control system 6 to actuator port P1 to move the piston 3 down. Similarly, hydraulic fluid may be sent from the control system to actuator port P2 to move the piston 3 up.
The control system 6 also includes a vent V into the sea where excess hydraulic fluid may be leaked out. For example, when the piston 3 goes up, the control system 6 dumps a corresponding volume of hydraulic fluid into the sea through the vent V. When in a vent mode, the control system 6 communicates with the seawater, and the hydraulic fluid within the control system 6 may become contaminated with seawater. Seawater, which contains corrosive chemicals such as chlorides, for example, can enter the spring chamber 12 of the actuator 2 and corrode the spring 4 and other parts of the actuator 2. If the spring 4 corrodes, this can cause failure of the actuator 2. Because the spring 4 is typically the most mechanically stressed component in the actuator 2, corrosion of the spring 4 may cause the spring 4 to fracture into a number of pieces. Failure of the spring 4 usually renders the actuator 2 inoperable for controlling a gate valve 8.
Furthermore, a hydraulic line from the control system must be provided into port P2 to supply a hydrostatic head underneath the piston 3 in order to achieve equilibrium. Each actuator 2 in use under the sea requires one hydraulic line from the control panel 6. In subsea applications, there are a limited number of hydraulic lines available for use.
As described above, prior art actuators 2 are not designed to accept seawater inside, which can corrode various components such as the spring 4. In an attempt to prevent seawater from entering hydraulic actuators, an external pressure compensator 10 can be coupled between the control system 6 and port P2 of the actuator 2, as shown in FIG. 1B. The external pressure compensator 10, also referred to herein as a piston accumulator or piston accumulator system, is a separate component from the actuator 2 and provides hydrostatic pressure compensation of hydraulic fluid displaced within the actuator 2 during operation. The pressure compensator 10 prevents seawater-contaminated hydraulic fluid from the control system 6 from entering port P2 in the actuator spring chamber 12, thus preventing corrosion of the spring 4.
However, external pressure compensators 10 are typically attached to the actuator 2 by brackets (not shown), for example, and are fluidly coupled to the actuator 2 by piping at P2. The connection joints of the piping provide potential leak sites, which may affect the reliability of the actuator system. Thus, a need exists for an actuator and compensator package that has fewer potential leak sites, to improve the reliability of the system.
Furthermore, using an external pressure compensator 10 is disadvantageous in that an additional component and installation is required, requiring increased cost and labor. Reliance on an additional manufacturer (e.g. for the pressure compensator 10) is required, and more engineering is required, to select the size, pressure rating and availability of the external compensator. Clamping and mounting the compensator 10 with the actuator 2 can be problematic, requiring more connections and leading to more leakage paths, so that a chance of seawater entering the spring chamber 12 is created.
The use of an external pressure compensator 10 also increases the space required. There may be space restrictions at the installation site for the actuator 2 that may make it difficult or unfeasible to use an actuator 2 with an external pressure compensator 10.
Embodiments of the present invention achieve technical advantages as a hydraulic actuator with a built-in pressure compensator. Hydraulic fluid that is possibly contaminated with seawater is prevented from entering the chamber containing the spring, preventing corrosion of the spring and extending the usable life of the actuator.
In accordance with one aspect of the present invention, a hydraulic actuator includes an actuator housing, a built-in pressure compensator, a first housing internal chamber, and a first hydraulic via. The built-in pressure compensator is located within the housing. The built-in pressure compensator includes a compensator cylinder portion, a compensator piston portion, a first compensator piston chamber, a second compensator piston chamber, and a compensator hydraulic port. The compensator cylinder portion is located within the actuator housing. The compensator cylinder portion is fixed relative to the housing and has an internal chamber formed therein. The compensator piston portion slidably fits within the compensator internal chamber.
The first compensator piston chamber is formed between a first side of the compensator piston portion and the compensator cylinder portion within the compensator internal chamber. The second compensator piston chamber is formed between a second side of the compensator piston portion and the compensator cylinder portion within the compensator internal chamber. The compensator hydraulic port is routed through the housing, with one end opening outside of the housing and the other end opening to the first compensator piston chamber. The first housing internal chamber is formed within the housing. The first hydraulic via is formed through the compensator cylinder portion, fluidly coupling the second compensator piston chamber with the first housing internal chamber.
In accordance with another aspect of the present invention, a hydraulic actuator is provided, which includes a housing, an operating stem, a first cylinder portion, a first housing internal chamber, a second housing internal chamber, a spring, a first piston portion, a first piston chamber, a second cylinder portion, a second piston portion, a second piston chamber, a third piston chamber, a first hydraulic port, a second hydraulic port, a first hydraulic via, and a second hydraulic via. The operating stem extends into the housing and is slidably coupled to the housing. The first cylinder portion slidably fits within the housing and has a first cylinder internal chamber formed therein with a closed end and an open end. The first cylinder portion is mechanically coupled to the operating stem. The first housing internal chamber is formed within the housing between the housing and the first cylinder portion at the open end of the first cylinder internal chamber, such that the first cylinder internal chamber of the first cylinder portion opens to the first housing internal chamber. The second housing internal chamber is formed within the housing between the housing and an exterior of the first cylinder portion. The spring is located within the housing and is biased between the housing and the first cylinder portion. The first piston portion is located within the housing, is fixed relative to the housing, extends through the open end of the first cylinder internal chamber, and slidably fits into the first cylinder internal chamber of the first cylinder portion. The first piston chamber is formed between the first piston portion and the first cylinder portion within the first cylinder internal chamber. The second cylinder portion is located within the housing and is fixed relative to the housing. The second cylinder portion has a second cylinder internal chamber formed therein. The second piston portion is located within the housing and slidably fits within the second cylinder internal chamber. The second piston chamber is formed between a first side of the second piston portion and the second cylinder portion within the second cylinder internal chamber. The third piston chamber is formed between a second side of the second piston portion and the second cylinder portion within the second cylinder internal chamber. The first hydraulic port routes through the first piston portion and the housing, with one end opening outside of the housing and another end opening to the first piston chamber. The second hydraulic port routes through the housing, with one end opening outside of the housing and another end opening to the second piston chamber. The first hydraulic via is formed through the second cylinder portion and fluidly couples the third piston chamber with the first housing internal chamber. The second hydraulic via is formed through the first cylinder portion and fluidly couples the first housing internal chamber with the second housing internal chamber.
In accordance with another aspect of the present invention, a method of manufacturing an actuator is disclosed. The method includes providing an actuator housing, and disposing a compensator cylinder portion within the actuator housing, the compensator cylinder portion being fixed relative to the housing and having a compensator internal chamber formed therein. A compensator piston portion is slidably fitted within the compensator internal chamber, wherein a first compensator piston chamber is formed between a first side of the compensator piston portion and the compensator cylinder portion, and wherein a second compensator piston chamber is formed between a second side of the compensator piston portion and the compensator cylinder portion. A hydraulic port is formed through the housing such that the hydraulic port opens to the first compensator piston chamber. A hydraulic via is formed through the compensator cylinder portion to fluidly couple the second compensator piston chamber with the first housing internal chamber. The compensator cylinder portion, compensator piston portion, hydraulic port and hydraulic via comprise a built-in pressure compensator.
Advantages of embodiments of the invention include providing a space-saving actuator with a pressure compensator built into the housing. Installation of the actuator to a valve is simplified, and no external accumulator unit is required. Because no external piping joints are required to connect the built-in compensator to the actuator, the actuator has fewer potential leak sites.